Abstract
In this letter, a new scheme called extended space index modulation (ESIM) is proposed and investigated. Different from previous works, both the signal constellation and index domains are exploited, and the performance of the spectral efficiency and the reliability can be further enhanced. Specifically, in the ESIM, an antenna index (AI) vector set is designed to convey more extra index bits, which consists of two AI vector subsets. The two AI vector subsets, which are respectively used to modulate the quadrature amplitude modulation (QAM) and secondary QAM (S-QAM) symbols, include the AI vectors having two non-zero elements from <inline-formula> <tex-math notation="LaTeX">$\{(1,1),(1,j),(j,1),(j,j)\}$ </tex-math></inline-formula> to activate two transmit antennas and the AI vectors having only one non-zero element equaling to “1” to activate one transmit antenna. Furthermore, the S-QAM constellation is designed to enhance the squared Minimum Euclidean Distance. Simulation results are provided to show a close match with analytical results particularly in the high signal-to-noise ratio (SNR) region and demonstrate that significant performance gain can be achieved in the proposed ESIM.
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